Synchronizing system

ABSTRACT

A system for and a method of synchronizing the movement of serially connected drive and driven fluid motors employed to move electrostatic coating devices across articles to be coated. The electrostatic devices coat the articles with a protective and/or decorative coating material. Valve means is connected to a source of fluid under pressure and to a fluid input port of the drive fluid motor to control the direction of movement of the fluid motors and hence control movement of the electrostatic devices cooperatively associated with the fluid motors. Means, cooperatively associated with the fluid motors, which reacts to an imbalance in the movement of the fluid motors so as to cause balanced movement of the fluid motors so that the movement of the driven fluid motor is substantially synchronized with the movement of the drive fluid motor.

United States Patent Probst et al.

[ Mar. 14, 1972 [54] SYNCHRONIZING SYSTEM [72] Inventors: Richard O. Probst; William W. Smith, both of lndianapolis, lnd.; Henry B. Lee,

21 Appl. No; 20,228

FOREIGN PATENTS OR APPLllCATlONS 517,314 1/1940 Great Britain ..60/97 P Primary Examiner-Edgar W. Geoghegan Attorney-Merrill N. Johnson, Harry E. Downer, David H. Badger and Charles W. Hoffmann [57] ABSTRACT A system for and a method of synchronizing the movement of serially connected drive and driven fluid motors employed to move electrostatic coating devices across articles to be coated. The electrostatic devices coat the articles with a protective and/or decorative coating material. Valve means is connected to a source of fluid under pressure and to a fluid input port of the drive fluid motor to control the direction of movement of the fluid motors and hence control movement of the electrostatic devices cooperatively associated with the fluid motors. Means, cooperatively associated with the fluid motors, which reacts to an imbalance in the movement of the fluid motors so as to cause balanced movement of the fluid motors so that the movement of the driven fluid motor is substantially synchronized with the movement of the drive fluid motor.

9 Claims, 3 Drawing Figures 2,462,580 2/1949 Watson..... 60/97 E X 2,487,402 11/1949 Watson 91/171 X 3,205,853 9/1965 Wampler et al. 118/631 X 3,387,757 6/1968 Gratfy et a1 ..91/171 X Meme math 14, *iPl jlfl 7 ,648,565

3 Sheets-Sheet 1 I ..I F/ j amvsmoas 56 RICHARD 0. PROBST HENRY 8. LEE WILLIAM W. SMITH Patented March 14, 1972 S Sheets-Sheet 2 1 I I I I I I l I I I I l I l I l I 72 I I l I I I I l I I I I l I -l mvsmoas I F I l I .J I I L 1:11:12: :::::::i

RICHARD O. PROBIST HENRY 8. LEE WILLIAM W. SMITH wanted! arch E4, 197

3 Sheets-Sheet 5 INVENTORS RICHARD O. PROBS HENRY B. LEE

WILLIAM W. SMI

SYNCHRONIZING SYSTEM The present invention relates to a system for and a method of synchronizing the movement of fluid motors, and more particularly, to a system for and a method of synchronizing or maintaining a substantially constant distance between electrostatic coating devices employed to emit a spray of electrostatically charged particles toward articles to be coated by such particles.

Devices employing electrostatic force are utilized in spray coating apparatus to more efficiently effect deposition of a spray of coating material particles upon articles. Electrostatic coating apparatus includes an atomizing device that causes a charged spray of coating material particles to be projected toward the articles to be coated. The charged spray of coating material particles is deposited on the articles which are, in automated finishing processes, carried past the atomizing devices by a conveyor to thereby provide the articles with a protective and/or decorative coating.

Articles of extended length present several coating problems. For example, the entire length of the article cannot be properly coated with a stationary atomizing device. How ever, the effective width of the spray projected from the atomizing device can be significantly increased by moving or reciprocating the atomizing device across the length of the article to thereby coat the article having an extended length with the protective and/or decorative coating material.

However, the cylinder and the piston rod used to move or reciprocate the electrostatic coating device across the length of the articles is of unusual length where the vertical length of the articles to be coated is about feet or more. For example, in order to properly coat articles having a vertical length of 25 feet, the length of the cylinder and associated piston rod used to move the electrostatic devices across the vertical length of the articles would be approximately 25 feet. It should be appreciated that coating of 25-foot articles should be undertaken in an area which readily accommodates a cylinder and piston rod each having a vertical length of about 25 feet and an expanded vertical length of approximately 50 feet. Generally, in order to conserve manufacturing space, the 25- foot cylinder is installed in a pit provided in the ground. However, the piston rod, when extended, must project 25 feet above the ground in order to properly coat the 25-foot articles.

A problem generally associated with mechanisms moving an electrostatic device over articles having, for example, a 25- foot vertical length is that the speed of the conveyorized line used to transport the articles past the electrostatic device must be such as to permit the mechanism to move the electrostatic device across the length of the article with speed sufficient to provide a high quality, substantially uniform film of coating material upon the articles. Therefore, the speed of the articles past the moving electrostatic device is determined, at least in part, by the length of the articles to be coated. It follows that the greater the vertical length of the articles to be coated, the less the speed of the conveyor transporting the articles past the moving or reciprocating electrostatic device.

The present invention permits an increase in the conveyor speed by providing a system for moving a plurality of substantially uniformly spaced apart electrostatic devices across at least part of the length of an article carried past the electrostatic devices. The electrostatic devices are vertically spaced apart in such a manner that the uppermost electrostatic device coats about the top half of an article while the lowermost electrostatic device coats about the lower half of the article. In order to facilitate the blending together of the adjacent spray patterns to thereby provide a quality finish and, with certain types of electrostatic coating devices, to prevent electrostatic field interference which may harmfully effect electrostatic atomization of the coating material, the electrostatic devices are maintained at a substantially uniform spaced apart distance by the system. Furthermore, the electrostatic coating devices should be so spaced apart as to substantially eliminate the possibility of the devices frictionally engaging one another in such a manner as to generate sparks of the type which may be capable of igniting solvents and the like. In order to maintain the movable electrostatic devices at a substantially uniform, spaced apart distance, the motors used to move (if reciprocate the electrostatic devices are synchronized.

It is, therefore, an object of the present invention to provide a system for and a method of synchronizingthe movement of fluid motors used to move electrostatic coating devices across the length of articles to be coated by a charged spray of coating material particles provided by the electrostatic devices. Another object of the present invention is to provide a system which detects and corrects the lead or lag distance between drive and driven fluid motors used to move electrostatic spray coating devices. Further objects of the present invention will become apparent upon further review of the specification, the appended claims and the drawings.

In the drawing:

FIG. 1 is a diagrammatic illustration of electrostatic coatings device whose movement across an article is controlled employing a synchronizing system of the present invention;

FIG. 2 is a schematic illustration of a system for synchronizing the movement of the electrostatic device shown in FIG. 1; and

FIG. 3 is a schematic illustration of another system for synchronizing the movement of the electrostatic devices shown in FIG. 1.

Generally speaking, the present invention relates to a system for and to a method of synchronizing the movement of serially connected drive and driven fluid motors having fluid input and output ports. The system includes means connected to a source of fluid under pressure and to the fluid input port of the drive fluid motor to control the direction of movement of the fluid motors. In addition, the system includes means which reacts to an imbalance in the movement of the fluid motors to cause a balanced movement of the fluid motors so that the driven fluid motor is synchronized with the movement of the drive fluid motor.

Referring now to FIG. 1 of the drawing, a coating station for spray coating articles is indicated by reference numeral 10. A plurality of articles 11 are suitably suspended from conveyor 12 by hanger 13. Each article may be a continuous article of extended length or several articles serially connected together in the vertical plane or a mixture of both. The articles are transported through the coating station 10 by conveyor 12 for the application to the surface thereof of a suitable protective and/or decorative coating material. The articles are transported through the coating station in such a manner as to move around atomizing devices 15 and 35 in a substantially circular fashion in the manner described in U.S. Pat. No. 2,808,343. The conveyor 12 is suitably grounded or earthed as shown at 14. It is seen that at least while articles 11 are in close proximity to the atomizing devices 15 and 35 of the coating station 10, the articles are at ground or earth potential. Ground or earth potential of the articles 11 provides the articles with a spray attracting potential.

The coating station 10 includes a pair of vertically movable atomizing devices 15 and 35. The atomizing devices 15 and 35 move on the vertical lines generally illustrated by the dotted line rectangles 22 and 42 respectively.

The atomizing device 15 includes a disk 16 having an edge spaced approximately 8 or more inches and preferably 8 to 20 inches from articles 11 moving in a substantially circular fashion around the peripheral edge of disk 16. The atomizing device 35 includes a disk 36 having a peripheral edge approximately 8 or more inches and preferably 8 to 20 inches from the articles 11. Disk 16 is rotatably driven by a suitable motor 17 such as an electric or air motor. Disk 36 is rotatably driven by a suitable motor 37 such as an electric or air motor. Disk 16 includes a centrally located aperture (not shown) in the face thereof which is connected to coating material source 19 by conduit 18. Disk 36 includes a centrally located aperture (not shown) in the face thereof which is connected to a coating material source 39 by conduit 38. Coating material is fed to each of the disks and is spread over the face of each disk as a thin film as the disks are rotated. Coating material particles are atomized from the edge of periphery of each disk.

A suitable direct current (DC) source 20, capable of providing up to lOO kv. or higher, has the ungrounded terminal thereof connected to the atomizing device in such a manner as to provide an electrostatic field between disk 16 and the articles 11 present in the coating station 10. The remaining terminal of source 20 is grounded or earthed. The source 20 may also have its ungrounded terminal thereof connected to atomizing device 35 in such a manner as to provide an electrostatic field between disk 36 and the articles 11 present in the coating station 10. It may be more convenient to connect atomizing device 35 to a separate direct current source.

Column 21, fabricated from an electrically insulative material, carries motor 17 and is suitably connected to the rod end of piston rod 24 of fluid motor 26. The piston rod 24 is movable within cylinder 25. The end of the piston rod 24 opposite the end of the rod connected to column 21 carries piston 23. The fluid motor 26 includes cylinder 25, piston rod 24 and the piston 23.

Column 41, fabricated from an electrically insulative material, carries motor 37 and is connected to the rod end of piston rod 44 of fluid motor 46. The piston rod 44 is movable within cylinder 45. The end of the piston rod 44 opposite the end of the rod connects to column 41 carries piston 43. The fluid motor 46 includes cylinder 45, the piston rod 44 and the piston 43.

Fluid port 54 formed in cylinder of fluid motor 26 and fluid port 54' formed in cylinder 45 of fluid motor 46 are connected to the output of synchronizing system 51 through fluid lines 57 and 58. Fluid port 57 formed in cylinder 25 of fluid motor 26 and fluid port 56 formed in cylinder 45 of fluid motor 46 are connected to the output of the synchronizing system 51 through fluid lines 53 and 55 respectively. The input of the synchronizing system 51 is connected to hydraulic fluid reservoir 50 through pump 52 and fluid line 106. The function of the synchronizing system 51 is to detect an im' balance in the movement between the serially connected fluid motors and to react to such imbalance and synchronize the movement ofthe serially connected fluid motors 26 and 46.

FIG. 2 shows an embodiment ofa synchronizing system 51 used to synchronize the movement of fluid motors 26 and 46. The input of the synchronizing system 51 is connected to the output of pump 52. The pump 52 may be any suitable pump such as a vane pump capable of supplying fluid under pressure to the fluid motors.

The input of the synchronizing system 51 includes a pressure relief valve 60 capable of releasing excessive pressure which may be developed during operation of the system. Excess pressure developed in the system is relieved by by-passing fluid to reservoir 50. The pressure relief valve 60 may include a spring bias 61 which returns the valve to its normal position upon release ofthe high or excessive pressure.

Pressure relief valve 60 is connected to the input of solenoid operated four-way valve 63 through fluid line 62. The solenoid operated four-way valve 63 includes solenoids 64 and 65. An output of the solenoid operated four-way valve 63 is connected to port 56 at the piston end of fluid operated motor 46 through fluid line 67, solenoid operated four-way valve 75 and fluid line 55. The solenoid operated four-way valve 75 includes solenoid 76 and a bias means such as spring 77. Another output of the solenoid operated four-way valve 63 is connected to port 56 at the piston end of fluid operated motor 26 through fluid line 66, counterbalance control valve 68, fluid line 74, solenoid operated four-way valve 70 and fluid line 53. The counterbalance control valve 68 includes a bias means such as spring 69. The solenoid operated four-way valve 70 includes solenoid 71 and a bias means such as spring 72.

Port 54 at the rod end of fluid motor 26 is connected to port 54' at the rod end of fluid motor 46 through fluid line 58. Port 54 at the rod end of fluid motor 26 is also connected to thd solenoid operated four-way valve 70 through fluid line at ii lustrated in FIG. 2. Port 54' at the rod end of fluid motor 46 is connected to solenoid operated four-way valve 75 through fluid line 57 in the manner illustrated in FIG. 2.

Cooperatively associated with fluid motor 26 are switehei 83 and 84. Switches 83 and 84 may be any suitable gleetrle switch mechanism which is capable of reacting to the position of the piston rod 24 of the fluid motor 26. Switch 83 is pie grammed so as to be actuated when the piston rod 24 reaches its desired maximum upward movement. Switch 84 is pro= grammed so as to be actuated when the piston rod 24 has at= tained its desired maximum downward movement.

Switches 81 and 82 are cooperatively associated with piston rod 44 of fluid motor 46. Switches 81 and 82 may be any suitable electric switch used to sense the position of piston rod 44 of fluid motor 46. Switch 82 is programmed so as to be actuated when piston rod 44 reaches its desired maximum downward displacement. Switch 81 is programmed so as to be actuated when the piston rod 44 reaches it maximum desired upward movement. It is noted that switches 82 and 83 may be used to regulate the stroke length of piston rods 44 and 24. Switches 81 and 84 are used to detect whether or not the piston rods are synchronized at the end of the stroke. Adjustably mounting switches 81 and 82 and switches 83 and 84 in cooperative relationship with piston rods 44 and 24 on a suitable support member (not shown) permits an operator to vary the stroke length travelled by piston rods 44 and 24 and hence vary the distance travelled by disks 36 and 16 across articles 11.

The switches 81 and 82 and switches 83 and 84 are connected to the appropriate solenoids of the solenoid operated four-way valve through suitable latching relays (not shown). The latching relays are not shown in the interest of more clearly showing the present invention and since, it is thought, that no novelty resides in the structure of the latching device, per se.

Having thus described the structural elements illustrated in FIG. 2, the operation of the system will be described.

Assuming that piston rods 24 and 44 of fluid motor 26 and 46, respectively, are appropriately spaced apart and hence synchronized and beginning their respective upward movement across article 11, pump 52 causes a fluid such as oil to be withdrawn from reservoir 50 and supplied under pressure to the piston end of fluid motor 26 through solenoid operated four-way valve 63 and solenoid operated four-way valve 70. The accumulation of fluid under pressure at the piston end of fluid motor 26 causes upward movement of piston rod 24 and its cooperatively associated disk 16. Fluid present in the rod end of fluid motor 26 is displaced therefrom through line 58 to the rod end of fluid motor 46. The accumulation of fluid under pressure at the rod end of fluid motor 46 causes an upward movement of piston rod 44 and its cooperatively associated disk 36. Fluid in the piston end of fluid motor 46 is displaced therefrom to reservoir 50 through the solenoid operated fourway valve 75 and the solenoid operated four-way valve 63.

When disk 36 approaches its desired maximum upward displacement, switch 81 is actuated. Shortly thereafter disk 16 reaches its desired maximum upward displacement and switch 83 is actuated. Assuming that switch 81 is actuated just prior to the actuation of switch 83, the synchronizing system 51 detects that the disks are appropriately spaced apart or synchronized and the system does not undertake action to alter the movement of the fluid operated motor 26 and fluid operated motor 46.

It should be noted that during the upward movement of fluid motors 26 and 46, fluid motor 26 is the drive motor and fluid motor 46 is the driven motor.

Upon sequential actuation of switch 81 and then switch 83 by the fluid motors 46 and 26 respectively, solenoid 64 of solenoid operated four-way valve 63 is activated thereby disconnecting the output of pump 52 from the piston end of fluid motor 26 and connecting the output of pump 52 to the piston end of fluid motor 46. The piston end of fluid motor 26 is now connected to the reservoir 50 through solenoid operated fourway valve 70, counterbalance valve 63 and the solenoid operated four-way valve 63. The pump 52 supplies fluid under pressure to the piston end of fluid motor 46 through solenoid operated four-way valve 63 and solenoid operated four-way valve 75. The fluid supplied under pressure to the piston end of fluid motor 46 causes a downward displacement of piston rod 44 and its cooperatively associated disk 36. Fluid present in the rod end of fluid motor 46 is displaced through line 58 to the rod end offluid motor 26. The accumulation offluid at the rod end of the fluid motor 26 initiates a downward displacement ofpiston rod 24 and its cooperatively associated disk 16. Fluid present in the piston end of fluid motor 26 is displaced therefrom to reservoir 50 through solenoid operated four-way valve 70, counterbalance valve 68 and solenoid operated fourway valve 63.

It should be noted that during the downward displacement of the piston rods and their cooperatively associated disks, fluid motor 46 is the drive fluid motor and fluid motor 26 is the driven fluid motor.

Sequential actuation of switch 84 and then switch 82 occurs when piston rods 44 and 24 respectively are synchronized and reach their desired maximum downward displacement. Assuming that switch 84 is actuated immediately prior to actuation of switch 82, the synchronizing system 51 shown in FIG. 2 detects a balanced or synchronized condition. Solenoid 65 of solenoid operated four-way valve 63 is activated by the switches 84 and 82 so that the piston end of fluid motor 26 is connected to the output of pump 52 and the piston end of fluid motor 46 is connected to reservoir 50. The upward movement of the piston rods 24 and 44 is repeated in the manner described above.

A purpose of the synchronizing system illustrated in FIG. 2 is to maintain the disks at a substantially constant spaced apart distance. Assuming that the cylinders of each of the fluid motors are of substantially the same size and that no leakage of fluid under pressure is experienced from the connected together rod ends of the fluid motors, the piston rods 24 and 44 of the fluid motors and their cooperatively associated disks l6 and 36 will be at a substantially constant spaced apart distance and therefore in synchronization. However, if leakage of fluid is experienced from the rod ends of one or both ofthe fluid motors, the leakage however small is accumulative and eventually the piston rods and their cooperatively associated disks will no longer be appropriately spaced apart. When the disks are no longer appropriately spaced apart, the fluid motors are not synchronized.

Assuming on the upstroke that disk 36 lags behind disk 16, switch 83 is activated prior to activation of switch 81 whereby indicating that disk 36 is not appropriately spaced from disk 16. Actuation of switch 83 prior to activation of switch 81 causes activation of solenoid 71 of solenoid operated four-way valve 70 to thereby disconnect the output of pump 52 from the iston end of fluid motor 26 and connects the pump to the rod end of fluid motor 46 and to the rod end offluid motor 26. It should be seen that fluid at the piston end of fluid motor 26 is substantially prevented from being displaced therefrom by the blocking action of solenoid operated four-way valve 70. Therefore, piston rod 24 and its cooperatively associated disk 16 are substantially retained at their present location while fluid under pressure is supplied by pump 52 to the rod end of the fluid motor 46 thereby causing continued upward movement of piston rod 44 and its cooperatively associated disk 36 until such time as fluid motor 46 causes activation of switch 81. Activation of switch 81 indicates that the disks are appropriately spaced apart and hence synchronized. Solenoid 64 of solenoid operated four-way valve 63 is then activated thereby disconnecting the output of the pump 52 from the rod ends of the fluid motors 26 and 46 and connecting the output of pump 52 to the piston end of fluid motor 46 and the piston rods and their cooperatively associated disks are displaced downwardly in the manner described hereinabove.

Assuming that the fluid operated motors 46 and 26 are not appropriately spaced apart; i.e., out of'synchronization, during the downstroke and that disk 36 leads the disk 16, switch 82 is activated prior to activation of switch 04. Activation of switch 82 prior to activation of switch 84 causes activation of solenoid 76 of solenoid operated four-way valve 75 to thereby disconnect the output of pump 52 from the piston end of fluid motor 46 and connect the output of the pump to the rod end of fluid motor 26 and the rod end of fluid motor 46. It is seen that activation of solenoid 76 to shift valve 75 terminates the exhaust of fluid under pressure from fluid operated motor 46 and causes fluid under pressure to be delivered to the rod end of fluid motor 26 and fluid to be displaced from the piston end of fluid motor 26 to the reservoir 50 through solenoid operated four-way valve 70, counterbalance valve 68 and solenoid operated four-way valve 63 to thereby bring fluid motor 26 into synchronization with fluid motor 46. Upon activation of switch 84 by fluid motor 26, the synchronizing system 51 detects that the disks 16 and 36 are appropriately spaced apart and hence synchronized. Solenoid operated fourway valve 63 is activated so as to connect the pump 52 to the piston end of fluid motor 26 and displace the piston rods in the upward direction in the manner described above.

it is seen that when the driven fluid motor lags behind the drive fluid motor at the end of a stroke the synchronizing system 51 detects this lag and corrects the lag by substantially terminating displacement of the drive fluid motor and continuing displacement of the driven fluid motor until such time as the cooperatively associated disks are again separated by the appropriate distance. it should be noted that such a correction resulting in synchronization of the piston rods and their cooperatively associated disks is made near the end of the upstroke and the downstroke.

Referring now to FIG. 3, another embodiment of the synchronizing system 51 is illustrated. The input to the synchronizing system 51 is connected to the output of pump 52 through fluidline 62. The input of the synchronizing system includes pressure relief valve 60 for releasing excessive pressure which may be developed during the operation offluid motors 26 and 46. Excessive pressure developed in the system will be relieved by shunting fluid around the pump 52 to reservoir 50. The pressure relief valve 60 may include a suitable bias means such as spring 61 which returns the valve to its nor mal position upon release of the excessive pressure.

Solenoid operated four-way valve 63 includes solenoids 64 and 65 and is connected to the output of the pump 52. One port of solenoid operated four-way valve 63 is connected to the piston end offluid motor 26 through fluid line 53. Another port of the solenoid operated four-way valve 63 is connected to the piston end of fluid motor 46 through fluid line 55.

Pump 92 is connected to the fluid reservoir 50 through line 106. The output of pump 92 is connected to the line 58, between the rod ends of fluid motor 26 and fluid motor 46, through solenoid operated four-way valve and line 91. It should be noted that the output of pump 92 is normally returned to reservoir 50 by the open center construction of valve 85 when this output is not required to effect synchronization. The solenoid operated four-way valve 85 includes spring biased solenoids 86 and 89. A pressure relief valve 93 is cooperatively associated with pump 92 in order to relieve excessive pressures which may be present in line 91. Counterbalance valve 95 is cooperatively associated with solenoid operated four-way valve 63 in the manner illustrated in FIG. 3.

Cooperatively associated with fluid motor 26 are switches 103 and 104. Switches 103 and 104 may be any suitable electric switch which is capable of reacting to the position of piston rod 24 of fluid motor 26. Switch 104 is programmed so as to be actuated when the piston rod 24 has reached its desired maximum downward movement. Switch 103 is programmed so as to be actuated when the piston rod 24 has reached its maximum upward movement.

Switches 101 and 102 are cooperatively associated with the piston rod 44 of fluid motor 46. Switches 101 and 102 may be any suitable electric switch used to react to the position of piston rod 44 of fluid motor 46. Switch 101 is programmed so as to be actuated when piston rod 44 attains its desired maximum upward movement. Switch 102 is programmed to be actuated when piston rod 44 reaches its desired maximum downward displacement. Adjustably mounting switches 101 and 102 in cooperative relationship with piston rod 44 and switches 103 and 104 with piston rod 24 on suitable support members (not shown) permits an operator to vary the stroke length traveled by piston rods 24 and 44 and hence vary the distance traveled by disks l6 and 36 across article 11.

Having thus described the structural elements illustrated in FIG. 3, the operation of the system will be described.

Assuming that piston rods 24 and 44 of fluid motors 26 and 46, respectively are appropriately spaced apart and hence synchronized and are beginning their respective upward movement, pump 52 supplies fluid under pressure to the piston end of fluid motor 26 through solenoid operated fourway valve 63. The accumulation of fluid at the piston end of fluid motor 26 initiates an upward movement of the piston rod 24 and its cooperatively associated disk 16. Fluid at the rod end of fluid operated motor 26 is displaced therefrom through line 58 to the rod end of fluid motor 46. The accumulation of fluid in the rod end of fluid motor 46 initiates an upward movement of piston rod 44 and its cooperatively associated disk 36. Fluid is displaced from the piston end of fluid motor 46 through solenoid operated four-way valve 63 to reservoir 50.

When disk 36 reaches the desired maximum upward displacement, switch 101 is actuated. Assuming that switch 101 is actuated and switch 103 has not been actuated, the synchronizing system 51 detects that the disks 16 and 36 are appropriately spaced apart and hence synchronized. Since the synchronizing system 51 detects a synchronized condition the system does not undertake corrective action.

It should be noted that during the upward displacement of piston rods 24 and 44, fluid motor 26 is the drive motor and fluid motor 46 is the driven motor.

Upon actuation ofswitch 101 by fluid motor 46, solenoid 64 of the solenoid operated four-way valve 63 is activated thereby disconnecting the output of pump 52 from the piston end of fluid motor 26 and connecting the output of the pump 52 to the piston end of fluid motor 46. The piston end of fluid motor 26 is now connected to the reservoir 50 by the solenoid operated four-way valve 63. The pump 52 supplies fluid under pressure to the piston end of fluid motor 46 through solenoid operated four-way valve 63. The fluid under pressure supplied by pump 52 to the piston end of fluid motor 46 initiates a downward displacement of the piston rod 44 and its cooperatively associated disk 36. Fluid present in the rod end of fluid motor 46 is displaced through line 58 to the rod end of fluid motor 26. The accumulation of fluid at the rod end of fluid motor 26 initiates a downward displacement of piston rod 24 and its cooperatively associated disk 16. Fluid is displaced from the piston end of fluid motor 26 to reservoir 50 through counterbalance valve 95 and four-way valve 63.

It should be noted that during the downward displacement of the piston rods and their cooperatively associated disks fluid motor 46 is the drive fluid motor and fluid motor 26 is the driven fluid motor.

Switch 102 is actuated when piston rod 44 reaches its desired maximum downward movement. Assuming that switch 102 is actuated prior to actuation of switch 104, the synchronizing system 51 shown in FIG. 3 detects a balanced or synchronized condition. Solenoid 65 of the solenoid operated four-way valve 63 is activated so that the piston end of fluid motor 26 is connected to the output of pump 52 and the piston end of fluid motor 46 is connected to reservoir 50. The upward movement of the piston rods 24 and 44 is repeated in the manner described above.

Assuming on the upstroke of piston rods 24 and 44 that piston rod 24 and its cooperatively associated disk 16 leads piston rod 44 and its disk 36 thereby causing activation of switch 103 prior to activation of switch 101, switch 103 causes activation of solenoid 86 so that auxiliary pump 92 provides fluid under pressure through solenoid operated four-way valve to the rod end of fluid motor 46' and fluid motor 26. Valve 85 is retained or latched in such a position so that pump 92 continues to supply fluid to the rod ends of the fluid motors until such time as reversal in direction of movement of the piston rods move the lower piston rod 24 from engagement with switch 103 thereby deactivatingsolenoid 86 and returning solenoid operated four-way valve 85 to its normal position as shown in FIG. 3. If the piston rod 44 contacts switch 101 prior to piston rod 24 contacting switch 103 the movement is synchronized and reversal in the direction of movement of the piston rods occurs in the manner outlined above.

Assuming on the downstroke of the piston rods 24 and 44 that the piston rod 24 and its cooperatively associated disk 26 leads piston rod 44 and its disk 36 thereby causing activation of switch 104, solenoid 89 activates solenoid operated fourway valve 85 to its left-hand position from that shown in FIG. 3 which allows fluid to be removed from line 58 through the solenoid operated four-way valve 85 to reservoir 50. Removal of the fluid from the rod ends of the fluid motors 26 and 46 continues until the piston rod 44 engages switch 102 at which time piston rod 24 disengages with switch 104 and solenoid operated four-way valve 85 returns to its neutral position as illustrated in FIG. 3. If the piston rod 44 engages switch 102 prior to piston rod 24 engaging with switch 104 reversal takes place as disclosed above and no correction of the spacing between the disks is undertaken.

It is seen that rod 44 strokes between switches 101 and 102 and that such switches control the reversal in the direction of movement of fluid motors 26 and 46. The piston rod 24 strokes between switches 103 and 104. Switch 103 detects and initiates correction for the piston rods being too closely spaced, and switch 104 detects and initiates correction for the piston rods being too far apart.

The synchronizing system illustrated in FIG. 3 has several advantages over the synchronizing system illustrated in FIG. 2. For example, the movement of the piston rods are not terminated as corrections in the spacing between disks [6 and 36 are made. Further, the synchronizing system in FIG. 3 can detect and correct both for too much fluid and not enough fluid in the rod ends of the fluid motors 26 and 46.

Although the electrostatic devices illustrated in FIG. 1 include disks 16 and 36, other types of electrostatic devices may be substituted therefor. For example, electrostatic devices using air, hydraulic force combination thereof and the like may be substituted for the illustrated disks. Suitable other types of electrostatic devices are illustrated in US. Pat. Nos. 3,169,882 and 3,169,883. Where electrostatic devices other than disks are used, the articles 11 will probably be transported past such electrostatic devices in a substantially straight line rather than in a substantially circular path as previously disclosed.

The coating material may be a fluid, semifluid or solid material. Where a fluid or semifluid material is used, it is applied to the surfaces of articles 11 in relatively thin layers which change to a solid coating with the passage of time. The change to a solid may or may not be reversible, and may occur by evaporation of solvent by chemical reaction, or by combination of the two. The solid material may be a thermoplastic powder such as polyvinylchloride, polyester and the like or a thermosetting powder such as epoxy and the like.

We claim:

I. An electrostatic coating apparatus including means to maintain electrostatic spray coating devices spaced apart and synchronized during displacement across articles to be coated, the means including fluid motors each having a piston and a pistonrod, the piston rods carrying the spray coating devices and being substantially axially aligned, the piston rod ends of each fluid motor being connected together so that fluid of the fluid motors flows therebetween during synchronized movement, means supplying fluid to the piston end of one of the fluid motors during synchronized movement causing the piston of the one fluid motor to be moved, movement of the piston and rod of the one fluid motor displacing fluid from the rod end of the one fluid motor to the rod end of the other fluid motor causing movement of the piston and rod of the other fluid motor and displacement of fluid from the piston end of the other fluid motor, and synchronizing means reacting to an imbalance between the movement of the rod ends of the fluid motors to synchronize the rod ends of the fluid motors.

2. An electrostatic coating apparatus as claimed in claim l wherein the synchronizing means for reacting to the im balance in the movement of the fluid motors includes means for governing the direction of movement of the fluid motors and for controlling the amount of movement of the fluid motors in a given direction.

3. An electrostatic coating apparatus as claimed in claim 1 wherein the means for reacting to the imbalance in the movement of the fluid motors includes means for disconnecting the means supplying fluid from the piston end of the one fluid motor and connecting the means supplying fluid to the rod end of the other fluid motor until the fluid motors are synchronized.

4. An electrostatic coating apparatus as claimed in claim 1 wherein the means for reacting to the imbalance in the movement of the fluid motors includes means for coupling means supplying fluid to the rod ends of the fluid motors when the movement of the other fluid motor lags behind the movement of the one fluid motor until the motors are synchronized, and

means for removing fluid from the rod end of the other fluid motor when the movement of the other fluid motor leads the movement of the one fluid motor until the motors are synchronized.

5. An electrostatic coating apparatus as claimed in claim 3 wherein the means for reacting to an imbalance in movement includes valve means for blocking fluid flow from the one fluid motor during synchronization of the other fluid motor with the one fluid motor.

6. A method of electrostatically coating articles including the steps of moving the pistons and piston rods of fluid motors each having a piston and a piston rod, the piston rods carrying spray coating devices and being substantially axially aligned, the piston rod ends of each fluid motor being connected together so that fluid of the fluid motors flows therebetween during synchronized movement,

alternately supplying fluid to the piston ends of the fluid motors during synchronized movement causing the piston and rod of one fluid motor to be :moved, movement of the piston and rod of the one fluid motor displacing fluid from the rod end of the one fluid motor to the rod end of the other fluid motor causing movement of the piston and rod of the other fluid motor and displacement of fluid from the piston end of the other fluid motor, and

reacting to an imbalance between the movement of the rod ends of the fluid motors to synchronize the rod ends of the fluid motors.

7. A method of electrostatically coating articles as claimed in claim 6 further including the step of controlling the amount of movement of the fluid motors in a given direction.

8. A method of electrostatically coating articles as claimed in claim 6 further including the step of disconnecting the supply fluid from the piston end of the one fluid motor and connecting the supply fluid to the rod end of the of the other fluid motor until the motors are synchronized.

9. A method of electrostatically coating articles as claimed in claim 6 further including the steps of coupling supply fluid to the rod end of the fluid motors when the movement of the other fluid motor lags behind the movement of the one fluid motor until the motors are synchronized or removing fluid from the rod end of the other fluid motor when the movement of the other fluid motor leads the movement of the one fluid motor until the motors are synchronized. 

1. An electrostatic coating apparatus including means to maintain electrostatic spray coating devices spaced apart and synchronized during displacement across articles to be coated, the means including fluid motors each having a piston and a piston rod, the piston rods carrying the spray coating devices and being substantially axially aligned, the piston rod ends of each fluid motor being connected together so that fluid of the fluid motors flows therebetween during synchronized movement, means supplying fluid to the piston end of one of the fluid motors during synchronized movement causing the piston of the one fluid motor to be moved, movement of the piston and rod of the one fluid motor displacing fluid from the rod eNd of the one fluid motor to the rod end of the other fluid motor causing movement of the piston and rod of the other fluid motor and displacement of fluid from the piston end of the other fluid motor, and synchronizing means reacting to an imbalance between the movement of the rod ends of the fluid motors to synchronize the rod ends of the fluid motors.
 2. An electrostatic coating apparatus as claimed in claim 1 wherein the synchronizing means for reacting to the imbalance in the movement of the fluid motors includes means for governing the direction of movement of the fluid motors and for controlling the amount of movement of the fluid motors in a given direction.
 3. An electrostatic coating apparatus as claimed in claim 1 wherein the means for reacting to the imbalance in the movement of the fluid motors includes means for disconnecting the means supplying fluid from the piston end of the one fluid motor and connecting the means supplying fluid to the rod end of the other fluid motor until the fluid motors are synchronized.
 4. An electrostatic coating apparatus as claimed in claim 1 wherein the means for reacting to the imbalance in the movement of the fluid motors includes means for coupling means supplying fluid to the rod ends of the fluid motors when the movement of the other fluid motor lags behind the movement of the one fluid motor until the motors are synchronized, and means for removing fluid from the rod end of the other fluid motor when the movement of the other fluid motor leads the movement of the one fluid motor until the motors are synchronized.
 5. An electrostatic coating apparatus as claimed in claim 3 wherein the means for reacting to an imbalance in movement includes valve means for blocking fluid flow from the one fluid motor during synchronization of the other fluid motor with the one fluid motor.
 6. A method of electrostatically coating articles including the steps of moving the pistons and piston rods of fluid motors each having a piston and a piston rod, the piston rods carrying spray coating devices and being substantially axially aligned, the piston rod ends of each fluid motor being connected together so that fluid of the fluid motors flows therebetween during synchronized movement, alternately supplying fluid to the piston ends of the fluid motors during synchronized movement causing the piston and rod of one fluid motor to be moved, movement of the piston and rod of the one fluid motor displacing fluid from the rod end of the one fluid motor to the rod end of the other fluid motor causing movement of the piston and rod of the other fluid motor and displacement of fluid from the piston end of the other fluid motor, and reacting to an imbalance between the movement of the rod ends of the fluid motors to synchronize the rod ends of the fluid motors.
 7. A method of electrostatically coating articles as claimed in claim 6 further including the step of controlling the amount of movement of the fluid motors in a given direction.
 8. A method of electrostatically coating articles as claimed in claim 6 further including the step of disconnecting the supply fluid from the piston end of the one fluid motor and connecting the supply fluid to the rod end of the of the other fluid motor until the motors are synchronized.
 9. A method of electrostatically coating articles as claimed in claim 6 further including the steps of coupling supply fluid to the rod end of the fluid motors when the movement of the other fluid motor lags behind the movement of the one fluid motor until the motors are synchronized or removing fluid from the rod end of the other fluid motor when the movement of the other fluid motor leads the movement of the one fluid motor until the motors are synchronized. 